1. Field of the Invention
The present invention relates to the formation of 1,3-diaryl triazenes, e.g., 1,3-diphenyltriazene, by the diazotization-coupling of primary aromatic monoamines, e.g., aniline.
2. Description of the Prior Art
1,3-Diaryl triazenes (also referred to as diazoamino aryl compounds) can be made to undergo rearrangement by heating, e.g., in the presence of a Friedel-Crafts catalyst, to form aromatic amino azo compounds. The latter are useful for the preparation of aromatic diamines by reduction with hydrogen. The diamines, in turn, are useful as intermediates in the preparation of polymers, antioxidants, etc.
U.S. Pat. No. 2,894,942 describes the formation of aromatic amino azo compounds by adding an inorganic nitrite to a mixture of an excess of a primary aryl monoamine, a mineral acid, and a Friedel-Crafts catalyst while the temperature is 0.degree.-50.degree. C. (20.degree.-30.degree. C. preferred), and thereafter heating up to about 40.degree.-75.degree. C. (45.degree.-55.degree. C. preferred). A portion of the amine is diazotized and the diazonium salt couples with unreacted amine to form the diazoamino aryl compound, which rearranges to the amino azo compound under the combined influence of the catalyst and heat. One of the disadvantages of this process, when considered in terms of large-scale operations, is the need for separating and disposing of the salt, e.g., sodium chloride, produced as a by-product of the diazotization reaction.
Over a period of a century or more, publications occasionally have appeared describing the diazotization of primary aromatic amines by the use of certain nitrogen oxides. For example, Griess, in 1862 (Ann. 121, No. 3, 257-280), reported the synthesis of diazoaminobenzene by passing what he called "a weak stream of nitrous acid" into a cold solution of aniline in alcohol until all of the aniline was consumed. Griess used the formula "NO.sub.3 " to denote the nitrous acid, but did not describe the composition or derivation of his diazotizing agent.
U.S. Pat. No. 2,622,078 (Klaassens et al.) describes carrying out the diazotization of amino aromatic sulfonic acids to diazonium compounds in water-ketone mixtures. Although nitrous gas (described as N.sub.2 O.sub.3 or a mixture of NO and NO.sub.2 of a composition approximating that of N.sub.2 O.sub.3) was disclosed to be useful in the Klaassens et al. process, the gas was introduced at 20.degree. C. into a mixture of acetone of butanone, water, and nitric acid, and the amino compound was added to the mixture while the temperature was maintained below 35.degree. C. Thus, Klaassens et al. used conditions which led to the formation of nitrous acid. Furthermore, Klaassens et al. operated with full consumption of their amine to produce the diazonium compound, and effected no coupling of the diazonium compound.
Lovejoy et al., J. Chem. Soc. (A) 1968, 2325-8, reported the formation of a diazonium nitrite by the reaction of a primary atomatic amine in an organic solvent with liquid, undissociated dinitrogen trioxide at -85.degree. C., as well as the isolation of a small amount of the diazoamino compound in some cases. However, the authors did not describe the action of gaseous nitrogen trioxide on the amines, nor did they disclose the conditions that would be required to produce a diazoamino compound as a major product.
The diazotization of aromatic amines by means of N.sub.2 O.sub.3 gas in the absence of water solvent, followed by coupling of the resulting diazo compound with phenols or naphthols also in the absence of water solvent is described in Japanese Patent Application Publication 15,631/61 (Sept. 7, 1961).
Primary aromatic amines also have been diazotized in solvents by means of pure nitrogen tetroxide. O. N. Witt, Tagbl. Natf.-Vers. Baden-Baden 1879, 194 (Chem. Zentr. 1880, II, 226) reported obtaining benzenediazonium nitrate by the reaction of anhydrous pure nitrogen tetroxide with aniline in an anhydrous benzene solution; and B. Houston et al., J. Am. Chem. Soc. 47, 3011-3018 (1925), obtained a diazoaminobenzene derivative as well as the corresponding diazonium nitrate by the action of pure, anhydrous nitrogen tetroxide on o-, m-, and p-nitroaniline in an anhydrous benzene solution.